Intermediates and improved processes for the preparation of neplanocin A

ABSTRACT

Intermediate compounds, including 2-(t-butyldimethylsilyloxymethyl)-3,4-[(dimethylmethylene)dioxy]-5-hydroxy-tricyclo[5.2.1.0 2,6 ]dec-8-ene, which are useful for the synthesis of neplanocin A having strong antitumor activity. Improved processes for the preparation of neplanocin A, starting from optically active 2-hydroxymethyl-5-hydroxy-tricyclo[5.2.1.0 2,6 ]deca-3,8-diene and via a key step comprising a retro-Diels-Alder reaction of the above intermediate.

[0001] This invention relates to compounds, including2-(t-butyldimethylsilyloxymethyl)-3,4-[(dimethylmethylene)-dioxy]-5-hydroxy-tricyclo[5.2.1.0^(2,6)]dec-8-eneand the analogues thereof, which are useful as intermediates for thesynthesis of neplanocin A having strong antitumor activity. Theinvention also relates to improved processes for the preparation ofneplanocin A.

BACKGROUND OF THE INVENTION

[0002] Neplanocin A is represented by the following formula and one ofcarbanucleosides having strong antitumor activity, but it is not itselfa sufficient drug for the clinical treatment of cancer, because of itsstrong adverse effect.

[0003] Nevertheless, there have been desired improved methods forefficiently preparing neplanocin A and related compounds.

[0004] Vandewalle et al. (Synlett, December 1991, 921-922) disclose thesynthesis of (−)-neplanocin A starting from L-ribulose in 14 steps andin 15% overall yield. Ohira et al. (Tetrahedron Letters, vol. 36, No. 9,pp. 1537-1538, 1995) disclose the synthesis of (−)-neplanocin A startingfrom D-ribose modified with the protecting group in 9 steps and in 12%overall yield. Trost et al. (Tetrahedron Letters, vol. 38, No. 10, pp.1707-1710, 1997) disclose the stereoselective synthesis of(−)-neplanocin A using an asymmetric catalyst in 13 steps and in 4%overall yield. Thus, the above prior processes require more improvementin the process step and yield.

SUMMARY OF THE INVENTION

[0005] The present invention provides a group of intermediates usefulfor the synthesis of neplanocin A and related compounds which improveour flexibility in exploring structural variation of carbanucleosideshaving potential use including chemotherapeutic agents.

[0006] The invention also relates to improved processes for thepreparation of neplanocin A in short process step and in high yield,starting from a compound of the following formula (1) and via a compoundof the following formula (6).

DETAILED DESCRIPTION OF THE INVENTION

[0007] The present invention provides new class of the compounds usefulas intermediates for the synthesis of neplanocin A, which includes thecompounds of the following formulas:

[0008] wherein R₁ and R₂ are independently hydrogen or an alkanoyl groupof 2-20 carbons;

[0009] wherein X is halogen;

[0010] wherein X is halogen and Y is a protecting group;

[0011] wherein X is halogen and Y is a protecting group;

[0012] wherein X is halogen and Y is a protecting group;

[0013] wherein Y is a protecting group;

[0014] wherein Y is a protecting group;

[0015] wherein Y is a protecting group;

[0016] wherein Y is a protecting group;

[0017] wherein Y is a protecting group.

[0018] Examples of the alkanoyl group of 2-20 carbons for R₁ and R₂include, but are not limited to, acetyl, propionyl, butyryl, isobutyryl,valeryl, isovaleryl, pivaloyl, lauroyl, myristoyl, palmitoyl, stearoyl,caproyl, enanthoyl, capryloyl and icosanoyl. Examples of the halogen forX are Cl, Br and I.

[0019] The protecting groups for Y can include any group known in theart of organic synthesis for the protection of hydroxyl groups. Examplesof such protecting group include, but are not limited, totrimethylsilyl, triethylsilyl, t-butyldimethylsilyl (TBS),t-butyldiphenylsilyl, methoxymethyl, methoxyethoxymethyl, t-butyl,benzyl, triphenylmethyl, isopropyldimethylsilyl, tribenzylsilyl andtriisopropylsilyl.

[0020] Specific compounds within formulas (2)-(10) are represented bythe following respective formulas (2a)-(10a):

[0021] wherein TBS stands for t-butyldimethylsilyl.

[0022] The present invention also provides a process for the preparationof neplanocin A which comprises the steps of: (a) reacting a compound offormula (1′)

[0023] with a halogenating agent, to form a compound of formula (2)

[0024] wherein X is halogen;

[0025] (b) reacting the compound (2) with an agent for the protection ofhydroxyl groups, to form a compound of formula (3)

[0026] wherein X is as defined above and Y is a protecting group;

[0027] (c) treating the compound (3) with an oxidizing agent, to form acompound of formula (4)

[0028] wherein X and Y are as defined above;

[0029] (d) reacting the compound (4) with a ketalizing agent, to form acompound of formula (5)

[0030] wherein X and Y are as defined above;

[0031] (e) treating the compound (5) with a dehalogenating agent, toform a compound of formula (6)

[0032] wherein Y is as defined above;

[0033] (f) subjecting the compound (6) to a retro-Diels-Alder reaction,to form a compound of formula (7)

[0034] wherein Y is as defined above;

[0035] (g) treating the compound (7) with an oxidizing agent, to form acompound of formula (8)

[0036] wherein Y is as defined above;

[0037] (h) reducing the compound (8) with a reducing agent, to form acompound of formula (9)

[0038] wherein Y is as defined above;

[0039] (i) subjecting the compound (9) to a Mitsunobu reaction, to forma compound of formula (10)

[0040] wherein Y is as defined above, followed by deprotection.

[0041] The process for the preparation of neplanocin A is illustratedbelow, in order of steps (a) to (i).

[0042] Step (a)

[0043] Depending on the halogenating agent and the solvent used, thereaction may be carried out at a temperature of about −20 to 20° C.,preferably about 0° C., for about 1 to 10 hrs, preferably 2 hrs. As areaction solvent may be used a halogenated hydrocarbon solvent such asdichloromethane, chloroform and dichloroethane. The halogenating agentssuch as brominating, chlorinating and iodinating agents are well knownin the art of organic synthesis. Examples of such halogenating agentsinclude, but are not limited, to HBr, diphos-Br₂, N-bromosuccinimide(NBS), thionyl bromide, HCl, diphos-Cl₂, N-chlorosuccinimide (NCS) andthionyl chloride.

[0044] Step (b)

[0045] The agents for the protection of hydroxyl groups (called“protecting agent” hereafter) may be selected from any agent known inthe art of organic synthesis for the protection of hydroxyl groups, forexample, but not limited to halides including chlorides or bromides oftrimethylsilyl, triethylsilyl, t-butyldimethylsilyl,t-butyldiphenylsilyl, methoxymethyl, methoxyethoxymethyl, t-butyl,benzyl, triphenylmethyl, isopropyldimethylsilyl, tribenzylsilyl,triisopropylsilyl or the like.

[0046] Depending on the protecting agent and solvent used, the reactionmay be carried out at a temperature of about −20 to 40° C., for about 10to 20 hrs. As a solvent may be used a base such as imidazole,benzimidazole, triethylamine, pyridine and hexamethylene disilazane. Abase for fixation of free halogenated hydrogen may also be used as thesolvent. Where the protecting agent is each kind of silyl chlorides andmethoxyethoxymethyl halides, the above-mentioned bases are used. Wherethe protecting agent is benzyl halides and methoxymethyl halides, sodiumhydride is used as the base. Where the hydroxyl group is protected witht-butyl group, the reaction is carried out with isobutene in thepresence of an acid type catalyst such as sulfuric acid.

[0047] Step (c)

[0048] The oxidizing agents used may be selected from any of a varietyof the agents known in the art of synthetic organic chemistry, forexample, but not limited to, osmium tetraoxide, potassium permanganate,lead tetraacetate, ruthenium tetraoxide and selenium dioxide+hydrogenperoxide, with osmium tetraoxide being most preferred.

[0049] Depending on the oxidizing agent and solvent used, the reactionmay be carried out at a temperature of about −20 to 40° C., for about 1to 30 hrs. As a reaction solvent may be used a polar solvent such aswater and tetrahydrofuran (THF). Where the oxidizing agent iscatalytically used, the reaction is carried out in the presence of anoxygen source such as methylmorpholine N-oxide.

[0050] Step (d)

[0051] The ketalizing agents may be selected from acetals such as2,2-dimethoxypropane, 2,2-diethoxypropane or the like.

[0052] Depending on the ketalizing agent, solvent and catalyst used, thereaction may be carried out at a temperature of about −20 to 40° C.,preferably around room temperature, for about 15 to 30 hrs. The reactionsolvents which may be used are relatively low boiling point solvents(excluding alcohols) among conventional solvents, such as acetone,methyl ethyl ketone, hydrocarbons, halogenated hydrocarbons, diethylether, diisopropyl ether and THF. The catalysts which may be used in thereaction are acid type catalysts such as hydrochloric acid, ammoniumchloride, p-toluene-sulfonic acid, pyridinium p-toluenesulfonate,aluminum chloride and an acid type ion-exchange resin.

[0053] Step (e)

[0054] The dehalogenating agents used may be selected from any of avariety of the agents known in the art of synthetic organic chemistry,for example, but not limited to, active zinc dust, magnesium, sodium,palladium, sodium iodide and potassium iodide.

[0055] Depending on the dehalogenating agent and solvent used, thereaction may be carried out under heat at reflux, for about 5 to 20 hrs.The reaction solvents which may be used are alcohols such as methanol,ethanol, propanol and isopropanol, with methanol being preferable.

[0056] Step (f)

[0057] The retro-Diels-Alder reaction used here refers to thermaldissociation of Diels-Alder adducts, occurring most readily when one orboth fragments are particularly stable (see, Organic Name Reactionsattached to The Merck Index, 12th Edn.) The reaction may be carried outunder heat at reflux in a high boiling point solvent, for about 20 to 60minutes. Such solvents are chemically stable, high boiling pointsolvents having a boiling point of 250 to 300° C. Diphenyl ether,α-chloronaphthalene, methyl α-naphthyl ether, ethyl α-naphthyl ether anddibenzyl ether are preferable.

[0058] Step (g)

[0059] The oxidizing agents may be selected from any of a variety of theagents known in the art of synthetic organic chemistry, for example, butnot limited to, chromic acid (VI), pyridinium dichromate, pyridiniumchlorochromate, chromium oxide (VI)—pyridine complex, manganese dioxide,dimethyl sulfoxide, hypohalorite and ruthenium tetraoxide.

[0060] Depending on the oxidizing agent and solvent used, the reactionmay be carried out at a temperature of about 0 to 30° C., for about 1 to10 hrs. The reaction solvents which may be used are any solvent if it isliquid in the neighborhood of the reaction temperature and is stable tothe oxidizing agent. Halogenated hydrocarbons are preferable, such asdichloromethane, 1,2-dichloroethane and chloroform.

[0061] Step (h)

[0062] The reducing agents may be selected from any of a variety of theagents known in the art of synthetic organic chemistry, for example, butnot limited to, diisobutylaluminum hydride, lithium aluminum hydride,triisobutylaluminum, trialkoxy derivatives of lithium aluminumhydroxide, sodium bis(2-methoxyethoxy)aluminum hydride, sodiumborohydride, trimethoxy sodium borohydride, lithium borohydride,tri-sec-butyl lithium borohydride and tri-sec-butyl potassiumborohydride.

[0063] Depending on the reducing agent and solvent used, the reactionmay be carried out at a temperature of about −78 to 0° C., for about 1to 5 hrs. The reaction solvents which may be used are any solvent if itis liquid at low temperature and is stable to the reducing agent.Toluene, benzene and THF are preferable.

[0064] Step (i)

[0065] The Mitsunobu reaction used here refers to condensation ofalcohols and acidic components on treatment with dialkylazodicarboxylates and trialkyl- or triarylphosphines occurring primarilywith inversion of configuration via the proposed intermediaryoxyphosphonium salts (see, Organic Name Reactions attached to The MerckIndex, 12 Edn.)

[0066] Depending on the reactant and solvent used, the reaction may becarried out at a temperature between 0° C. and room temperature, forabout 4 to 12 hrs. The reaction solvents which may be used are anysolvent if it is good solvent inert to the starting compound used in theMitsunobu reaction and the resulting compound, and is liquid in theneighborhood of the reaction temperature. THF and 1,3-dioxane arepreferable.

[0067] The deprotection in step (i) can be carried out in conventionalmanner.

[0068] The present invention-also provides a process for preparing anoptically active compound of formula (1′)

[0069] which comprises subjecting a racemic compound of formula (11)

[0070] to a transesterification with an acylating agent in the presenceof a hydrolase to optically resolve the racemic compound into anoptically active diester of formula (12)

[0071] wherein R₃ is an alkyl group of 1-19 carbons, and a monoester offormula (13)

[0072] wherein R₃ is as defined above, followed by alcoholysis.

[0073] The transesterification can be carried out under conventionalconditions with an acylating agent which has an acyl group of R₃COO (R₃is an alkyl group of 1-19 carbons) in the presence of a hydrolase.Examples of the alkyl groups of 1-19 carbons include, but are notlimited to, methyl, ethyl, propyl, isopropyl, butyl, sec-butyl,tert-butyl, pentyl, heptyl, octyl, nonyl, dodecyl, tridecyl, tetradecyl,pentadecyl, hexadecyl, heptadecyl, octadecyl and nonadecyl.

PREFERRED EMBODIMENTS OF THE INVENTION

[0074] The processes of the present invention can be performed asdiscussed below. When the designated compounds show either one ofenantiomers in the optically active compounds, it is marked with theprime mark (′) except for the case of the compound (1′).

[0075] The compound of formula (11) in a racemic form which can be usedas a starting material in the present processes may be prepared byreducing the compound (16) prepared by Zwanenburg et al.'s method(Tetrahedron, 1985, 41, 963). As shown in the following scheme A, thecompound (16) may be prepared by epoxidizing the compound (14) withaqueous hydrogen peroxide followed by a Favorskii rearrangement. TheFavorskii rearrangement refers to a base-catalyzed rearrangement ofα-haloketones or α,β-epoxyketones to acids or esters. The compound (14)is formed from a Diels-Alder reaction of cyclopentadiene and1,4-benzoquinone which are easily available. The compound (16) isreduced with diisobutylaluminum hydride (DIBAL), thus leading to thecompound (11).

[0076] The resulting racemic compound (11) can be optically resolvedinto the corresponding optically active diester (12) and monoester (13),by the transesterification with the acylating agent in the presence ofthe hydrolase. The hydrolases which can be used herein, include, but arenot limited to, lipase, esterase, protease and lipoprotein lipase. Thosehydrolases may be any of animal, plant and fungus origins and may becommercially available immobilized products or dried extracts. Thoseoriginated from pseudomonas, candida and pancreatin are preferable. Theacylating agents which can be used in the present process include, butare not limited to, fatty acid anhydrides, fatty acid esters or thelike. More specifically, triglyceride, acetic anhydride, fatty acidtrichloroethyl esters, fatty acid isopropenyl esters and fatty acidvinyl esters can be used, and fatty acid vinyl esters are especiallypreferable. The reaction solvents which can be used include ethers,alkanes, benzene derivatives, halogenated hydrocarbon solvents, e.g.,acetonitrile, acetone, dimethylformamide (DMF), dimethyl sulfoxide(DMSO), diethyl ether, diisopropyl ether and t-butyl methyl ether.Diethyl ether, diisopropyl ether and t-butyl methyl ether arepreferable. The reaction temperature is in the range of −20° C. to 200°C., preferably 20° C. to 40° C. The reaction time is in the range of 1to 20 hrs., preferably 5 to 8 hrs. The treatment for purification afterreaction can use general separation method such as silica gel columnchromatography after the hydrolase is filtered off, by which eachcompound can be isolated and obtained.

[0077] As shown in the following scheme B, the resulting opticallyactive diester (12′) and monoester (13′) can be subjected to thealcoholysis with an alcohol e.g., methanol in the presence of a suitablebase such as potassium carbonate, thus leading to the optically activediol (1′).

[0078] The (+)-form of the resulting diol (1′) can lead to(−)-neplanocin A, and the (−)-form of the diol (1′) can lead to(+)-neplanocin A.

[0079] The process for preparing (−)-neplanocin A is discussed below,but (+)-neplanocin A which is its enantiomer can be prepared in asimilar manner, starting from the (−)-form of the diol (1′).

[0080] The (+)-form of the diol (1′) is reacted with a brominating agentsuch as N-bromosuccinimide to afford(+)-9-bromo-2-hydroxymethyl-5,8-epoxytricyclo[5.2.1.0^(2,6)]dec-3-ene(2a′). It is preferable that the reaction solvent uses halogenatedhydrocarbon solvents such as dichloromethane. The reaction temperatureis in the range of −20° C. to 20° C., preferably about 0° C. Thereaction time is in the range of 1 to 10 hrs., preferably 2 hrs.

[0081] The above compound (2a′) and t-butyldimethylsilyl chloride arereacted for 10-20 hrs in the presence of a suitable base such asimidazole to afford(+)-9-bromo-2-t-butyldimethylsilyloxymethyl-5,8-epoxytricyclo[5.2.1.0^(2,6)]dec-3-ene (3a′) wherein the primary hydroxyl group in the compound (2a′)is protected with t-butyldimethylsilyl group.

[0082] The compound (3a′), because of taking a cage stereostructure, canbe treated with a suitable oxidizing agent such as osmium tetraoxide,thus leading stereoselectively and regiospecifically to(+)-9-bromo-2-t-butyldimethylsilyloxymethyl-3,4-dihydroxy-5,8-epoxytricyclo[5.2.1.0^(2,6)]decane(4a′).

[0083] The reaction of two hydroxyl groups newly formed in said compound(4a′) with dimethoxypropane affords(+)-9-bromo-2-t-butyldimethylsilyloxymethyl-3,4-[(dimethyl-methylene)dioxy]-5,8-epoxytricyclo[5.2.1.0^(2,6)]decane(5a′).

[0084] The compound (5a′) is treated with active zinc powder to afford(+)-2-t-butyldimethylsilyloxymethyl-3,4-[(dimethylmethylene)dioxy]-5-hydroxy-tricyclo[5.2.1.0^(2,6)]dec-8-ene(6a′).

[0085] The compound (6a′) can be heated to reflux in diphenyl ether orcan be subjected to a flush vacuum thermolysis to induce aretro-Diels-Alder reaction, thus leading to(−)-(1R,4R,5S)-3-(t-butyldimethylsilyloxymethyl)-4,5-[(dimethylmethylene)dioxy]-2-cyclopentene-1-ol(7a′).

[0086] The treatment of the hydroxyl group in the compound (7a′) with asuitable oxidizing agent such as pyridinium dichromate and pyridiniumchlorochromate affords(−)-(4R,5S)-3-(t-butyldimethylsilyloxymethyl)-4,5-[(dimethylmethylene)dioxy]-2-cyclopentene-1-one(8a′).

[0087] Reduction of the compound (8a′) with a reducing agent such asdiisobutyl aluminum hydride, lithium aluminum hydride or the like canlead stereospecifically to(+)-(1S,4R,5S)-3-(t-butyldimethylsilyloxymethyl)-4,5-[(dimethyl-methylene)dioxy]-2-cyclopentene-1-ol(9a′) wherein the hydroxyl group at the 1-position of the compound (7a′)is inversed.

[0088] Combining the compound (9a′) with adenine by a Mitsunobu reactioncan lead to(−)-(1′R,4′R,5′S)-3′-(t-butyldimethylsilyloxymethyl)-4′,5′-[(dimethylmethylene)-dioxy]-2‘-cyclopentene-1’-yl]adenine(10a′). Finally, the compound (10a′) is deprotected using a purificationmethod with an ion-exchange resin to afford (−)-neplanocin A.

[0089] The invention is further illustrated by the following Examples.These examples are presented to exemplify the invention and are not tobe construed as limiting the invention's scope.

REFERENTIAL EXAMPLE 1

[0090] A solution of tricyclo[6.2.1.0^(2,7)]undeca-4,9-diene-3,6-dione(14) (26.13 g, 150 mmol) in acetone (100 ml) was cooled to 0° C. on anice-bath. To the solution was added saturated aqueous NaHCO₃ (33 ml). Tothe mixture was added dropwise 34.5% aqueous hydrogen peroxide (142 ml)while keeping at 0° C. After the addition, the reaction mixture wasstirred at 0° C. for 1 hr and then water (100 ml) was added. From themixture solution, the product was extracted with diethyl ether (total700 ml). The extract was washed with saturated aqueous NaCl and driedover magnesium sulfate, and the solvent was distilled off under reducedpressure to afford as the residue4,5-epoxy-tricyclo[6.2.1.0^(2,7)]undec-9-ene-3,6-dione (15) (28.06 g,148 mmol, 98.35% yield) in light yellowish white crystals.

REFERENTIAL EXAMPLE 2

[0091] A suspension of4,5-epoxy-tricyclo[6.2.1.0^(2,7)]undec-9-ene-3,6-dione (15) (9.28 g,48.8 mmol) in ethanol (50 ml) was heated to 45° C. To the suspension wasadded dropwise a 5 M-ethanol solution of sodium hydroxide (18 ml) over aperiod of 30 minutes. From the reaction mixture, ethanol was distilledoff under reduced pressure. The residue was dissolved with diethyl ether(300 ml), washed with saturated aqueous NaCl and dried over magnesiumsulfate, and diethyl ether was distilled off under reduced pressure toafford as the residue5-oxo-tricyclo[5.2.1.0^(2,6)]deca-3,8-diene-2-carboxylate (16) (6.58 g,30.1 mmol, 61.78% yield) in dark brown liquid.

EXAMPLE 1

[0092] A solution of ethyl5-oxo-tricyclo[5.2.1.0^(2,6)]deca-3,8-diene-2-carboxylate (16) (1.84 g,8.43 mmol) in toluene (30 ml) was cooled to −78° C. under an argonatmosphere and stirred. To the reaction solution was added dropwise a1.5 M-toluene solution of diisobutylaluminum hydride (DIBAL) (19.7 ml,29.5 mmol) over a 25 minute period. The reaction mixture was stirred for3 hrs while keeping at −78° C. and aqueous ammonia was added whilecooling. The precipitated solid was filtered off through a glass funnel.The filtrate was concentrated under reduced pressure to afford 2.08 g ofthe residue (white solid) which was then subjected to silica gel columnchromatography (eluting solvent: n-hexane/ethyl acetate=1/1) to afford2-hydroxymethyl-5-hydroxy-tricyclo[5.2.1.0^(2,6)]deca-3,8-diene (11)(0.98 g, 5.5 mmol, 65% yield), with the following data:

[0093] IR (neat): ν=3270 cm⁻¹

[0094]¹H NMR (CDCl₃): δ=1.60 (1H, d, J=8.8 Hz), 1.68 (1H, d, J=8.8 Hz),2.70 (2H, m), 2.96 (1H, s), 3.67 (1H, d, J=10.6 Hz), 3.84 (1H, d, J=10.6Hz), 4.76 (1H, s), 5.53 (1H, dd, J=5.5, 1.8 Hz).

EXAMPLE 2

[0095] A suspension of2-hydroxymethyl-5-hydroxy-tricyclo[5.2.1.0^(2,6)]deca-3,8-diene (11)(980 mg, 5.5 mmol) and vinyl acetate (758 mg, 8.8 mmol) in t-butylmethyl ether (3 ml) was stirred at room temperature. To the reactionsolution was added lipase (1 g, immobilized lipase originated frompseudomonas, manufactured by Toyobo Co., Ltd.) and the mixture wasstirred at room temperature for 8 hrs. Lipase was filtered off and thefiltrate was concentrated under reduced pressure to afford a yellowresidue. The residue was subjected to silica gel column chromatography(eluting solvent: n-hexane/ethyl acetate=3/1) to afford the diacetate(12′) (590 mg, 2.25 mmol) and the monoacetate (13′) (495 mg, 2.25 mmol),respectively, with the following data:

[0096] For (−)-diacetate (12′)

[0097] IR (neat): ν=2967, 1734 cm⁻¹

[0098]¹H NMR (CDCl₃): δ 1.52 (1H, d, J=8.8 Hz), 1.60 (1H, d, J=8.8 Hz),1.99 (3H, s), 2.01 (3H, s), 2.69 (1H, br s), 2.74 (1H, br s), 4.07 (1H,d, J=10.7 Hz), 4.34 (1H, d, J=10-0.7 Hz), 5.50 (2H, m), 5.95 (2H, m)

[0099] MS: m/z=262 (M+). Anal. Calcd. for C15H18O4 (M+): m/z=262.1205.Found: m/z=262.1203.

[0100] For (+)-monoacetate (13′)

[0101] IR (neat): ν=3440, 2962, 1730 cm⁻¹

[0102]¹H NMR (CDCl₃): δ=1.60 (1H, d, J=8.8 Hz), 1.68 (1H, d, J=8.8 Hz),2.05 (3H, s), 2.64 (1H, m), 2.78 (1H, br s), 2.94 (1H, br s), 4,12 (1H,d. J=10.7 Hz), 4.36 (1H, d, J=10.7 Hz), 4.76 (1H, d, J=10.2 Hz), 5.54(1H, d, J=1.4 Hz), 5.59 (1H, d, J=1.4 Hz), 5.92 (1H, m), 6.16 (1H, m)

[0103] MS: m/z=220 (M+). Calcd. for C13H16O3 (M+): m/z=220.1099. Found:m/z=220.1104.

[0104] To a solution of the resultant diacetate (12′) (590 mg) inmethanol (20 ml) was added potassium carbonate (691 mg, 5.0 mmol) andthe mixture was stirred at room temperature for 8 hrs. The reactionproduct was extracted with ethyl acetate (40 ml). The organic layer waswashed with saturated aqueous NaCl, dried over magnesium sulfate andconcentrated under reduced pressure to afford(−)-2-hydroxymethyl-5-hydroxy-tricyclo[5.2.1.0^(2,6)]deca-3,8-diene (330mg, 1.85 mmol) having the following specific rotation:

[0105] [α]_(D) ²⁶ −168.11° (cl. 03, EtOH).

[0106] According to a conventional method, further, this compound wasled to the dibenzoate which was analyzed with an optical resolutioncolumn (Chiral Cell OD manufactured by Daicel Co., Ltd.,5%-isopropanol-n-hexane solution), by which it was found 92% ee.

[0107] For the monoacetate (13′), similar procedure was carried outexcept for using 373 mg(2.7 mmol) of potassium carbonate, therebyaffording(+)-2-hydroxymethyl-5-hydroxy-tricyclo[5.2.1.0^(2,6)]deca-3,8-diene (367mg, 2.06 mmol) having the following specific rotation and melting point:

[0108] [α]_(D) ³⁰ +154.86° (cl. 01, EtOH), m.p. 116-119° C.

[0109] According to a conventional method, further, this compound wasled to the dibenzoate which was analyzed with an optical resolutioncolumn (Chiral Cell OD manufactured by Daicel Co., Ltd.,5%-isopropanol-n-hexane solution), by which it was found >99% ee.

EXAMPLE 3

[0110] A solution of(+)-2-hydroxymethyl-5-hydroxy-tricyclo[5.2.1.0^(2,6)]deca-3,8-diene((+)-form of Compound (1′)) (287 mg, 1.6 mmol) obtained in Example 2 indichloromethane (30 ml) was cooled to 0° C. and stirred. To the solutionwas added N-bromosuccinimide (322 mg, 1.8 mmol) and the mixture wasstirred for 2 hrs while keeping at 0° C. The reaction solution wasconcentrated under reduced pressure and the resulting residue wassubjected to silica gel column chromatography (eluting solvent:n-hexane/ethyl acetate=2/1) to afford(+)-9-bromo-2-hydroxymethyl-5,8-epoxytricyclo-[5.2.1.0²⁶]dec-3-ene (2a′)(414 mg, 1.6 mmol, 99.6% yield), with the following data:

[0111] [α]^(D) ²⁹ +153.15° (c0.302, CHCl₃)

[0112] IR (neat): ν=3409, 2972 cm⁻¹

[0113]¹H NMR (CDCl₃): δ=1.73 (1H, br), 2.17-2.38 (1H, m), 3.48 (2H, d),4.08 (1H, d), 4.56-4.69 (3H, m), 5.70 (1H, m), 6.0 (1H, m)

[0114] MS: m/z=256 (M+). Calcd. for C11H13BrO2 (M+): m/z=256.0098.Found: m/z=256.0112.

EXAMPLE 4

[0115] To a solution of(+)-9-bromo-2-hydroxymethyl-5,8-epoxytricyclo[5.2.1.0^(2,6)]dec-3-ene(2a′) (319 mg, 1.24 mmol) and imidazole (126.5 mg, 1.86 mmol) in DMF (30ml) was added t-butyldimethylsilyl chloride (242 mg, 1.6 mmol), and themixture was stirred overnight at room temperature and diluted withn-hexane (80 ml). The organic layer was washed with saturated aqueousNaCl, dried over magnesium sulfate and concentrated under reducedpressure to obtain the residue. Silica gel column chromatography(eluting solvent: n-hexane/diethyl ether=2/1) of the residue afforded(+)-9-bromo-2-(t-butyldimethylsilyloxymethyl)-5,8-epoxytricyclo[5.2.1.0^(2,6)]dec-3-ene (3a′) (447 mg,1.20 mmol, 97% yield), with the following data:

[0116] [α]^(D) ²⁸ +114.060 (c0.161, CHCl₃)

[0117] IR (neat): ν=2954, 2856, 1471, 1377 cm⁻¹

[0118]¹H NMR (CDCl₃): δ=0.013 (6H, s), 0.86 (9H, s), 2.16-2.38 (2H, m),2.39-2.65 (3H, m), 3.40 (1H, d, J=10.0 Hz), 3.77 (1H, d, J=10.0 Hz),4.13 (1H, d, J=2.5 Hz), 4.61 (2H, m), 5.77 (1H, d, J=5.7 Hz), 5.95 (1H,dd, J=5.7, 2.5 Hz)

[0119] MS: m/z=355 (M+-Me). Calcd. for C16H24BrO2Si (M+-Me):m/z=355.0763. Found: m/z=355.0729.

EXAMPLE 5

[0120] A solution of(+)-9-bromo-2-(t-butyldimethyl-silyloxymethyl)-5,8-epoxytricyclo[5.2.1.0^(2,6)]dec-3-ene(3a′) (283 mg, 0.762 mmol) in a mixed solvent of THF (15 ml) and water(5 ml) was cooled to 0° C. and stirred. To the solution were added4-methylmorpholine N-oxide (155 mg, 1.14 mmol) and a 0.197 M-THFsolution of osmium tetraoxide (1.5 ml, 0.3 mmol). Subsequently, themixture was allowed to warm up to room temperature and stirredovernight. A 10% aqueous solution of sodium sulfite (15 ml) was addedand the mixture was filtered through Celite. The filtered product waswashed thoroughly with water, THF and diethyl ether. The combinedwashings and filtrate were diluted with diethyl ether (80 ml). Theorganic layer was washed with saturated aqueous NaHCO₃ and saturatedaqueous NaCl, respectively, and dried over magnesium sulfate.Subsequently, the solvent was distilled off under reduced pressure toobtain the residue. Silica gel column chromatography (eluting solvent:n-hexane/diethyl ether=2/1) of the residue afforded(+)-9-bromo-2-(t-butyldimethylsilyloxymethyl)-3,4-dihydroxy-5,8-epoxytricyclo[5.2.1.0^(2,6)]decane(4a′) (246 mg, 0.607 mmol, 80% yield), with the following data:

[0121] [α]D²⁸ +57.15° (c0.26, CHCl₃)

[0122] 1H NMR (CDCl₃): δ=0,099 (6H, s), 0.89 (9H, s), 1.65 (1H, brs),1.95 (1H, d, J=10.9 Hz), 2.16-2.38 (2H, m), 2.37 (2H, m), 2.62 (1H, t,J=4.4 Hz), 2.77 (1H, m), 3.05 (1H, d, J=5.2 Hz), 3.51 (1H, d, J=5.5 Hz),3.60 (1H, d, J=10.2 Hz), 3.81 (1H, d, J=9.9 Hz), 4.15 (2H, m), 4.39 (1H,t, J=4.9 Hz), 4.53 (1H, d, J=4.9 Hz)

[0123] MS: m/z=389 (M+-Me). Calcd. for C16H26BrO4Si (M+-Me):m/z=389.0318. Found: m/z=389.0397.

EXAMPLE 6

[0124] To a solution of(+)-9-bromo-2-(t-butyldimethyl-silyloxymethyl)-3,4-dihydroxy-5,8-epoxytricyclo[5.2.1.0^(2.6)]-decane(4a′) (186 mg, 0.459 mmol) in acetone (30 ml) were addeddimethoxypropane (72 mg, 0.69 mmol) and pyridinium p-toluenesulfonate(15 mg) and the mixture was stirred overnight at room temperature. Tothe reaction solution was added diethyl ether (50 ml) and the mixturewas washed with saturated aqueous NaHCO₃ and saturated aqueous NaCl.This solution was dried over magnesium sulfate and concentrated underreduced pressure to obtain the residue. Silica gel column chromatography(eluting solvent: n-hexane/ethyl acetate=3/1) of the residue afforded(+)-9-bromo-2-(t-butyldimethylsilyloxymethyl)-3,4-[(dimethylmethylene)dioxy]-5,8-epoxytricyclo[5.2.1.0^(2,6)]decane(5a′) (205 mg, 0.46 mmol), 100% yield), with the following data:

[0125] [α]_(D) ²⁹ +73.150 (c0.12, CHCl₃)

[0126] IR (neat): ν=2928, 2855, 1471, 1380 cm⁻¹

[0127]¹H NMR (CDCl₃): δ=0.023 (6H, s), 0.86 (9H, s), 1.24 (3H, s), 1.41(3H, s), 2.02-2.19 (2H, m), 2.36 (1H, m), 2.69 (1H, m), 3.47 (1H, d,J=9.9 Hz), 3.63 (1H, d, J=2.5 Hz), 3.98 (1H, d, J=9.6 Hz), 4.37 (1H, d,J=5.7 Hz), 4.54 (1H, m), 4.60 (1H, d, J=5.5 Hz)

[0128] MS: m/z=429 (M+-Me). Calcd. for C19H30BrO4Si (M+-Me):m/z=429.1131. Found: m/z=429.1090.

EXAMPLE 7

[0129] To a solution of(+)-9-bromo-2-(t-butyldimethyl-silyloxymethyl)-3,4-[(dimethylmethylene)dioxy]-5,8-epoxy-tricyclo[5.2.1.0^(2,6)]decane(5a′) (205 mg, 0.46 mmol) in methanol (30 ml) were added active zincpowder (182 mg, 2.76 mmol) and acetic acid (0.1 ml), and the mixture washeated to reflux for 10 hrs. The reaction solution was filtered throughCelite and the filtered mass was washed with methanol. The combinedwashings and filtrate were diluted with diethyl ether (80 ml) and washedwith saturated aqueous NaHCO₃ and saturated aqueous NaCl. This solutionwas dried over magnesium sulfate and concentrated under reduced pressureto afford(+)-2-(t-butyldimethylsilyloxymethyl)-3,4-[(dimethylmethylene)dioxy]-5-hydroxy-tricyclo[5.2.1.0^(2,6)]dec-8-ene (6a′) (160 mg, 0.44 mmol, 95% yield) in colorless powderycrystals, with the following data:

[0130] [α]_(D) ³⁰ +147.00 (c0.30, CHCl₃)

[0131] IR (Nujol): ν=3313, 2924, 2854, 1462, 1376 cm⁻¹

[0132]¹H NMR (CDCl₃): δ=0.023 (6H, s), 0.87 (9H, s), 1.18 (3H, s), 1.41(4H, m), 1.58 (1H, m), 1.78 (1H, brs), 2.40 (1H, m), 2.86 (1H, s), 3.05(1H, s), 3.52 (1H, d, J=9.6 Hz), 3.99 (1H, d, J=4.9 Hz), 4.07-4.12 (3H,m), 6.20 (1H, m), 6.32 (1H, m)

[0133] MS: m/z=366 (M+). Calcd. for C20H34O4Si (M+): m/z=366.2226.Found: m/z=366.2242.

EXAMPLE 8

[0134] A solution of(+)-2-(t-butyldimethyl-silyloxymethyl)-3,4-[(dimethylmethylene)dioxy]-5-hydroxy-tricyclo[5.2.1.0^(2,6)]dec-8-ene(6a′) (280 mg, 0.76 mmol) in diphenyl ether (5 ml) was heated to refluxfor 30 minutes. The reaction solution was subjected to silica gel columnchromatography (eluting solvent: n-hexane/diethyl ether=1/1) to afford(−)-(1R,4R,5S)-3-(t-butyldimethylsilyloxymethyl)-4,5-[(dimethylmethylene)dioxy]-2-cyclopenten-1-ol(7a′) (225 mg, 0.749 mmol, 98.7% yield), with the following data:

[0135] [α]_(D) ³² −21.53° (c0.54, CHCl₃)

[0136] IR (neat): ν=3405, 2930, 2857, 1372 cm⁻¹

[0137]¹H NMR (CDCl₃): δ=0.086 (6H, s), 0.92 (9H, s), 1.36 (6H, d, J=11.2Hz), 1.98 (1H, d, J=6.3 Hz), 4.33 (2H, m), 4.55 (1H, d, J=5.8 Hz), 4.72(1H, m), 5.13 (1H, d, J=5.8 Hz), 5.75 (1H, d, J=1.1 Hz)

[0138] MS: m/z=285 (M+-Me). Calcd. for C14H25O4Si (M+-Me): m/z=285.1557.Found: m/z=285.1502.

EXAMPLE 9

[0139] To a solution of(−)-(1R,4R,5S)-3-(t-butyldimethylsilyloxymethyl)-4,5-[(dimethylmethylene)dioxy]-2-cyclopenten-1-ol(7a′) (225 mg, 0.749 mmol) in dichloromethane (50 ml) was addedpyridinium dichromate (425 mg, 1.13 mmol) and the mixture was stirred atroom temperature for 2 hrs. The reaction solution was filtered throughCelite and the filtrate was concentrated under reduced pressure toobtain the residue. Silica gel column chromatography (eluting solvent:n-hexane/diethyl ether=1/1) of the residue afforded(−)-(4R,5S)-3-(t-butyldimethyl-silyloxymethyl)-4,5-[(dimethylmethylene)dioxy]-2-cyclopenten-1-one(8a′) (186 mg, 0.623 mmol, 83% yield), with the following data:

[0140] [α]_(D) ²⁹ −10.670 (c0.85, CHCl₃).

[0141] IR (neat): ν=2955, 2931, 2857, 1725 cm⁻¹

[0142]¹H NMR (CDCl₃): δ=0.076 (6H, s), 0.89 (9H, s), 1.38 (6H, s),4.41-4.68 (3H, m), 5.03 (1H, d, J=5.8 Hz), 6.14 (1H, t, J=1.9 Hz) MS:m/z=283 (M+-Me). Calcd. for C14H23O4Si (M+-Me): m/z=283.14. Found:m/z=283.1377.

EXAMPLE 10

[0143] A solution of(−)-(4R,5S)-3-(t-butyldimethyl-silyloxymethyl)-4,5-[(dimethylmethylene)dioxy]-2-cyclopenten-1-one(8a′) (186 mg, 0.623 mmol) in toluene (10 ml) was cooled to −78° C. Tothe solution was added dropwise a 1.5 M-toluene solution ofdiisobutylaluminum hydride (0.62 ml, 0.93 mmol), and the mixture wasstirred at −78° C. for 2 hrs. The reaction solution diluted withmethanol and water, respectively was extracted with chloroform. Theorganic layer was washed with saturated aqueous NaCl, dried overmagnesium sulfate and concentrated under reduced pressure. The residuewas subjected to silica gel column chromatography (eluting solvent:n-hexane/diethyl ether=1/1) to afford(+)-(1S,4R,5S)-3-(t-butyldimethyl-silyloxymethyl)-4,5-[(dimethylmethylene)dioxy]-2-cyclopenten-1-ol(9a′) (186 mg, 0.62 mmol, 100% yield), with the following data:

[0144] [α]_(D) ²⁹ +22.530 (c0.63, CHCl₃).

[0145] IR (neat): ν=2954, 2930, 2857, 1372 cm⁻¹

[0146]¹H NMR (CDCl₃): δ=0.05 (6H, s), 0.89 (9H, s), 1.38 (6H, d, J=8.8Hz), 2.65 (1H, d, J=10.2 Hz), 4.17-4.35 (2H, m), 4.52 (1H, m), 4.74 (1H,m), 4.87 (1H, m), 5.71 (1H, t, J=0.8 Hz)

[0147] MS: m/z=285 (M+-Me). Calcd. for C14H25O4Si (M+-Me): m/z=285.1557.Found: m/z=285.1529.

EXAMPLE 11

[0148] A solution of(+)-(1S,4R,5S)-3-(t-butyldimethyl-silyloxymethyl)-4,5-[(dimethylmethylene)dioxy]-2-cyclopenten-1-ol(9a′) (145 mg, 0.48 mmol), adenine (272 mg, 1.92 mmol) andtriphenylphosphine (529 mg, 2.02 mmol) in THF (90 ml) was cooled to 0°C. To the cooled solution was added dropwise diisopropylazodicarboxylate (408 mg, 2.02 mmol), and the mixture was allowed towarm up to room temperature and stirred for 8 hrs. The reaction solutionwas concentrated under reduced pressure and the resulting residue wassubjected to silica gel column chromatography (eluting solvent:chloroform/ethanol=10/1) to afford (−)-[(1′R,4′R,5S)-3′-(t-butyldimethylsilyloxymethyl)-4′,5′-[(dimethylmethylene)dioxy]-2‘-cyclopentene-1’-yl]adenine(10a′) (148 mg, 0.40 mmol, 84% yield), with the following data:

[0149] [α]_(D) ²⁹ 31.57° (c0.29, CHCl₃)

[0150] IR (neat): ν=3322, 3171, 2954, 2931, 2857, 1645, 1597 cm

[0151]¹H NMR (CDCl₃): δ=0.10 (6H, s), 0.92 (9H, s), 1.35 (3H, s), 1.48(3H, s), 4.43 (2H, m), 4.70 (1H, d, J=5.8 Hz), 5.31 (1H, d, J=5.2 Hz),5.59(1H, m), 5.75 (1H, s), 5.78 (2H, brs), 7.68 (1H, s), 8.39 (1H, s)MS: m/z=412 (M+-Me). Calcd. for C19H28N5O3Si (M+-Me): m/z=402.1996.Found: m/z=402.1935.

EXAMPLE 12

[0152] A solution of(−)-[(1′R,4′R,5′S)-3′-(t-butyldimethylsilyloxymethyl)-41,5′-[(dimethylmethylene)-dioxy]-2′-cyclopentene-1′-yl]adenine(10a′) (138 mg, 0.33 mmol) in a mixed solvent of methanol (20 ml) and1N-hydrochloric acid (20 ml) was stirred at room temperature for 3 hrs.The reaction solution was concentrated under reduced pressure, and theresulting residue was dissolved in water (1 ml) and passed through anion exchange resin column (Dowex 50, H⁺ form). This column was washed bypassing pure water therethrough and then eluted with 5% aqueous ammonia.The resulting eluate was concentrated under reduced pressure to obtainwhite crystals. Recrystallization from methanol afforded (−)-NeplanocinA (78 mg, 0.30 mmol, 90% yield), with the following physical values:

[0153] [60 ]^(D) ²⁹ 31.57° (c0.29, CHCl₃), m.p. 217-219° C.

[0154] These values agreed closely with those given in the literature.

INDUSTRIAL APPLICABILITY

[0155] According to the present invention, there can be preparedoptically active2-hydroxymethyl-5-hydroxy-tricyclo[5.2.1.0^(2,6)]deca-3,8-diene (1′)which is a chiral element useful in the organic synthesis. The presentinvention can also provide the process for efficiently preparingneplanocin A in 10 steps and in 45% overall yield, starting from thecompound (1′).

What is claimed is:
 1. A compound of formula (1)

wherein R₁ and R₂ are independently hydrogen or an alkanoyl group of2-20 carbons.
 2. A compound of formula (2)

wherein X is halogen.
 3. A compound of claim 2 wherein X is Br.
 4. Acompound of formula (3)

wherein X is halogen and Y is a protecting group.
 5. A compound of claim4 wherein X is Br and Y is t-butyldimethylsilyl.
 6. A compound offormula (4)

wherein X is halogen and Y is a protecting group.
 7. A compound of claim6 wherein X is Br and Y is t-butyldimethylsilyl.
 8. A compound offormula (5)

wherein X is halogen and Y is a protecting group.
 9. A compound of claim8 wherein X is Br and Y is t-butyldimethylsilyl.
 10. A compound offormula (6)

wherein Y is a protecting group.
 11. A compound of claim 10 wherein Y ist-butyldimethylsilyl.
 12. A compound of formula (7)

wherein Y is a protecting group.
 13. A compound of claim 12 wherein Y ist-butyldimethylsilyl.
 14. A compound of formula (8)

wherein Y is a protecting group.
 15. A compound of claim 14 wherein Y ist-butyldimethylsilyl.
 16. A compound of formula (9)

wherein Y is a protecting group.
 17. A compound of claim 16 wherein Y ist-butyldimethylsilyl.
 18. A compound of formula (10)

wherein Y is a protecting group.
 19. A compound of claim 18 wherein Y ist-butyldimethylsilyl.
 20. A process for preparing an optically activecompound of formula (1′)

which comprises subjecting a racemic compound of formula (11)

to a transesterification with an acylating agent in the presence of ahydrolase to optically resolve the racemic compound into an opticallyactive diester of formula (12)

wherein R₃ is an alkyl group of 1-19 carbons, and a monoester of formula(13)

wherein R₃ is as defined above, followed by alcoholysis.
 21. A processof claim 20 wherein the acylating agent is a fatty acid vinyl ester. 22.A process of claim 20 wherein the hydrolase is originated frompseudomonas.
 23. A process of claim 20 wherein the acylating agent is afatty acid vinyl ester and the hydrolase is originated from pseudomonas.24. A process for the preparation of neplanocin A which comprises thesteps of: (a) reacting a compound of formula (1′)

with a halogenating agent, to form a compound of formula (2)

wherein X is halogen; (b) reacting the compound (2) with an agent forthe protection of hydroxyl groups, to form a compound of formula (3)

wherein X is as defined above and Y is a protecting group; (c) treatingthe compound (3) with an oxidizing agent, to form a compound of formula(4) (4)

wherein X and Y are as defined above; (d) reacting the compound (4) witha ketalizing agent, to form a compound of formula (5)

wherein X and Y are as defined above; (e) treating the compound (5) witha dehalogenating agent, to form a compound of formula (6)

wherein Y is as defined above; (f) subjecting the compound (6) to aretro-Diels-Alder reaction, to form a compound of formula (7)

wherein Y is as defined above; (g) treating the compound (7) with anoxidizing agent, to form a compound of formula (8)

wherein Y is as defined above; (h) reducing the compound (8) with areducing agent, to form a compound of formula (9)

wherein Y is as defined above; (i) subjecting the compound (9) to aMitsunobu reaction, to form a compound of formula (10)

wherein Y is as defined above, followed by deprotection.
 25. A processfor preparing a compound of formula (7)

wherein Y is a protecting group, which comprises subjecting a compoundof formula (6)

wherein Y is a protecting group, to a retro-Diels-Alder reaction.